Inverters for industrial use, home electric appliances, and the like include semiconductor apparatus such as a power module having a power semiconductor element mounted therein. Particularly, a semiconductor apparatus having a trench-gate type IGBT (Insulated Gate Bipolar Transistor) mounted therein is being widely used for its excellent controllability and energy saving.
The trench-gate type IGBT includes a trench gate that is formed in stripes on a surface of a semiconductor substrate having a p-type base layer formed on a surface layer portion of an n-type drift layer and is formed in such a manner as to penetrate the p-type base layer and reach the n-type drift layer. In contact with a side surface(s) of one or some of the trench gates, an n-type emitter layer is formed to form a channel in the p-type base layer on the side surface(s) of the trench gate(s) that is in contact with the n-type emitter layer. On the side surface(s) of the other trench gate(s), no n-type emitter layer is formed, to accumulate holes (positive holes) in the p-type base layer(s) in contact with the side surface(s) when the trench-gate type IGBT is switched on. The so-called dummy trench gate is a trench gate on a side surface of which no n-type emitter layer is formed and thus no channel is formed. On the other hand, the so-called active trench gate is a trench gate that has a channel formed on a side surface thereof and has a gate voltage applied thereto from a gate driving circuit. Further, the so-called active dummy trench gate is a particular dummy trench gate to which the gate voltage is applied from the gate driving circuit in the same manner as in the active trench gate.
In a trench-gate type IGBT as a conventional semiconductor apparatus, one or some dummy trench gates are connected to a gate terminal to be made into active dummy trench gates and the other dummy trench gate(s) is connected to an emitter terminal to be made into dummy trench gates. This has increased parasitic capacitance between a gate and a collector than in a case in which the active dummy trench gates are not connected to the gate terminal. Therefore, gate resistance is decreased to give rate of change in collector voltage with respect to time (dV/dt) at the time of turn-on of the IGBT, at the same level as conventional cases, thus decreasing a rate of change in collector current with respect to time (dI/dt) so that a turn-on loss has been reduced under a constant dV/dt (for example, see Patent Document 1).